Syed Ali - Academia.edu (original) (raw)
Papers by Syed Ali
Cognitive radios are promising solutions to the problem of overcrowded and inefficient licensed s... more Cognitive radios are promising solutions to the problem of overcrowded and inefficient licensed spectrum. In this work we explore the throughput potential of cognitive communication. We summarize different cognitive radio techniques that underlay, overlay and interweave the transmissions of the cognitive user with those of the licensed users. Recently proposed models for cognitive radios based on the overlay technique are described. For the interweave technique, we present a 'two switch' cognitive radio model and develop inner and outer bounds on the secondary radio capacity. Using the two switch model, we investigate the inherent tradeoff between the sensitivity of primary detection and the cognitive link capacity. With numerical results, we compare the throughputs achieved by the secondary user in the different models.
We show that the sum capacity of the K user frequency selective (or time-varying) interference ch... more We show that the sum capacity of the K user frequency selective (or time-varying) interference channel is C(SNR) = (K/2) log(SNR) +o(log(SNR)) meaning that the channel has a total of K/2 degrees of freedom per orthogonal time and frequency dimension. Linear schemes of interference alignment and zero forcing suffice to achieve all the degrees of freedom and multi-user detection is not required.
We consider the capacity of a narrowband point to point communication system employing multiple-e... more We consider the capacity of a narrowband point to point communication system employing multiple-element antenna arrays at both the transmitter and the receiver with covariance feedback. Under covariance feedback the receiver is assumed to have perfect Channel State Information (CSI) while at the transmitter the channel matrix is modeled as consisting of zero mean complex jointly Gaussian random variables with known covariances. Specifically we assume a channel matrix with i.i.d. rows and correlated columns, a common model for downlink transmission. We determine the optimal transmit precoding strategy to maximize the Shannon capacity of such a system. We also derive closed form necessary and sufficient conditions on the spatial covariance for when the maximum capacity is achieved by beamforming. The conditions for optimality of beamforming agree with the notion of waterfilling over multiple degrees of freedom.
IEEE Transactions on Information Theory, 2005
In this correspondence, we consider the problem of maximizing sum rate of a multiple-antenna Gaus... more In this correspondence, we consider the problem of maximizing sum rate of a multiple-antenna Gaussian broadcast channel (BC). It was recently found that dirty-paper coding is capacity achieving for this channel. In order to achieve capacity, the optimal transmission policy (i.e., the optimal transmit covariance structure) given the channel conditions and power constraint must be found. However, obtaining the optimal transmission policy when employing dirty-paper coding is a computationally complex nonconvex problem. We use duality to transform this problem into a well-structured convex multiple-access channel (MAC) problem. We exploit the structure of this problem and derive simple and fast iterative algorithms that provide the optimum transmission policies for the MAC, which can easily be mapped to the optimal BC policies.
Seminars in Cancer Biology, 2001
SV40 large T antigen (TAg) is a powerful oncoprotein capable of transforming a variety of cell ty... more SV40 large T antigen (TAg) is a powerful oncoprotein capable of transforming a variety of cell types. The transforming activity of TAg is due in large part to its perturbation of the retinoblastoma (pRB) and p53 tumor suppressor proteins. In addition, TAg binds to several other cellular factors, including the transcriptional coactivators p300 and CBP, which may contribute to its transformation function. Several other features of TAg that appear to contribute to its full transformation potential are yet to be completely understood. Study of TAg therefore continues to provide new insights into the mechanism of cellular transformation.
Journal of Neurochemistry, 2002
Abstract: The present study was undertaken to investigate whether the relatively selective neuron... more Abstract: The present study was undertaken to investigate whether the relatively selective neuronal nitric oxide synthase (NOS) inhibitor, 7-nitroindazole (7-NI), protects against methamphetamine (METH)-induced neurotoxicity. Male Swiss Webster mice received the following treatments (i.p.; q 3 h × 3): (a) vehicle/saline, (b) 7-NI (25 mg/kg)/saline, (c) vehicle/METH (5 mg/kg), and (d) 7-NI (25 mg/kg)/METH (5 mg/kg). On the second day, groups (a) and (b) received two vehicle injections, and groups (c) and (d) received two 7-NI injections (25 mg/kg, each). Administration of vehicle/METH resulted in 68, 44, and 55% decreases in the concentration of dopamine, 3,4-dihydroxyphenylacetic acid, and homovanillic acid, respectively, and a 48% decrease in the number of [3H]mazindol binding sites in the striatum compared with control values. Treatment with 7-NI (group d) provided full protection against the depletion of dopamine and its metabolites and the loss of dopamine transporter binding sites. Administration of 7-NI/saline (group b) affected neither the tissue concentration of dopamine and its metabolites nor the binding parameters of [3H]mazindol compared with control values. 7-NI had no significant effect on animals' body temperature, and it did not affect METH-induced hyperthermia. These findings indicate a role for nitric oxide in methamphetamine-induced neurotoxicity and also suggest that blockade of NOS may be beneficial for the management of Parkinson's disease.
IEEE Journal on Selected Areas in Communications, 2007
We explore the SNR-optimal relay functionality in a memoryless relay network, i.e. a network wher... more We explore the SNR-optimal relay functionality in a memoryless relay network, i.e. a network where, during each channel use, the signal transmitted by a relay depends only on the last received symbol at that relay. We develop a generalized notion of SNR for the class of memoryless relay functions. The solution to the generalized SNR optimization problem leads to the novel concept of minimum mean square uncorrelated error estimation(MMSUEE).
Cognitive radios are promising solutions to the problem of overcrowded and inefficient licensed s... more Cognitive radios are promising solutions to the problem of overcrowded and inefficient licensed spectrum. In this work we explore the throughput potential of cognitive communication. We summarize different cognitive radio techniques that underlay, overlay and interweave the transmissions of the cognitive user with those of the licensed users. Recently proposed models for cognitive radios based on the overlay technique are described. For the interweave technique, we present a 'two switch' cognitive radio model and develop inner and outer bounds on the secondary radio capacity. Using the two switch model, we investigate the inherent tradeoff between the sensitivity of primary detection and the cognitive link capacity. With numerical results, we compare the throughputs achieved by the secondary user in the different models.
We show that the sum capacity of the K user frequency selective (or time-varying) interference ch... more We show that the sum capacity of the K user frequency selective (or time-varying) interference channel is C(SNR) = (K/2) log(SNR) +o(log(SNR)) meaning that the channel has a total of K/2 degrees of freedom per orthogonal time and frequency dimension. Linear schemes of interference alignment and zero forcing suffice to achieve all the degrees of freedom and multi-user detection is not required.
We consider the capacity of a narrowband point to point communication system employing multiple-e... more We consider the capacity of a narrowband point to point communication system employing multiple-element antenna arrays at both the transmitter and the receiver with covariance feedback. Under covariance feedback the receiver is assumed to have perfect Channel State Information (CSI) while at the transmitter the channel matrix is modeled as consisting of zero mean complex jointly Gaussian random variables with known covariances. Specifically we assume a channel matrix with i.i.d. rows and correlated columns, a common model for downlink transmission. We determine the optimal transmit precoding strategy to maximize the Shannon capacity of such a system. We also derive closed form necessary and sufficient conditions on the spatial covariance for when the maximum capacity is achieved by beamforming. The conditions for optimality of beamforming agree with the notion of waterfilling over multiple degrees of freedom.
IEEE Transactions on Information Theory, 2005
In this correspondence, we consider the problem of maximizing sum rate of a multiple-antenna Gaus... more In this correspondence, we consider the problem of maximizing sum rate of a multiple-antenna Gaussian broadcast channel (BC). It was recently found that dirty-paper coding is capacity achieving for this channel. In order to achieve capacity, the optimal transmission policy (i.e., the optimal transmit covariance structure) given the channel conditions and power constraint must be found. However, obtaining the optimal transmission policy when employing dirty-paper coding is a computationally complex nonconvex problem. We use duality to transform this problem into a well-structured convex multiple-access channel (MAC) problem. We exploit the structure of this problem and derive simple and fast iterative algorithms that provide the optimum transmission policies for the MAC, which can easily be mapped to the optimal BC policies.
Seminars in Cancer Biology, 2001
SV40 large T antigen (TAg) is a powerful oncoprotein capable of transforming a variety of cell ty... more SV40 large T antigen (TAg) is a powerful oncoprotein capable of transforming a variety of cell types. The transforming activity of TAg is due in large part to its perturbation of the retinoblastoma (pRB) and p53 tumor suppressor proteins. In addition, TAg binds to several other cellular factors, including the transcriptional coactivators p300 and CBP, which may contribute to its transformation function. Several other features of TAg that appear to contribute to its full transformation potential are yet to be completely understood. Study of TAg therefore continues to provide new insights into the mechanism of cellular transformation.
Journal of Neurochemistry, 2002
Abstract: The present study was undertaken to investigate whether the relatively selective neuron... more Abstract: The present study was undertaken to investigate whether the relatively selective neuronal nitric oxide synthase (NOS) inhibitor, 7-nitroindazole (7-NI), protects against methamphetamine (METH)-induced neurotoxicity. Male Swiss Webster mice received the following treatments (i.p.; q 3 h × 3): (a) vehicle/saline, (b) 7-NI (25 mg/kg)/saline, (c) vehicle/METH (5 mg/kg), and (d) 7-NI (25 mg/kg)/METH (5 mg/kg). On the second day, groups (a) and (b) received two vehicle injections, and groups (c) and (d) received two 7-NI injections (25 mg/kg, each). Administration of vehicle/METH resulted in 68, 44, and 55% decreases in the concentration of dopamine, 3,4-dihydroxyphenylacetic acid, and homovanillic acid, respectively, and a 48% decrease in the number of [3H]mazindol binding sites in the striatum compared with control values. Treatment with 7-NI (group d) provided full protection against the depletion of dopamine and its metabolites and the loss of dopamine transporter binding sites. Administration of 7-NI/saline (group b) affected neither the tissue concentration of dopamine and its metabolites nor the binding parameters of [3H]mazindol compared with control values. 7-NI had no significant effect on animals' body temperature, and it did not affect METH-induced hyperthermia. These findings indicate a role for nitric oxide in methamphetamine-induced neurotoxicity and also suggest that blockade of NOS may be beneficial for the management of Parkinson's disease.
IEEE Journal on Selected Areas in Communications, 2007
We explore the SNR-optimal relay functionality in a memoryless relay network, i.e. a network wher... more We explore the SNR-optimal relay functionality in a memoryless relay network, i.e. a network where, during each channel use, the signal transmitted by a relay depends only on the last received symbol at that relay. We develop a generalized notion of SNR for the class of memoryless relay functions. The solution to the generalized SNR optimization problem leads to the novel concept of minimum mean square uncorrelated error estimation(MMSUEE).